Portable electronic devices such as laptops, tablet computers and personal multimedia devices are often configured to receive power from the AC/DC mains adapter or from an integrated battery pack. This integrated battery pack may contain multiple battery cells to provide sufficient power for the electronic device. During operation, battery cells are charged and discharged by a charging circuit. A protection circuit is often provided to protect the battery cells from improper use, for example, to prevent lithium-ion batteries from being overheated or overcharged. Furthermore, deeply discharging a lithium-ion battery may short-circuit the cell, thereby making a subsequent recharging of the cell unsafe.
Oftentimes, each individual cell within the battery pack may have a different charge capacity. This different charge capacity may be different intentionally by construction or through production tolerances and/or aging. For small capacity differences, balancing circuitry is often included in battery pack management circuits in order to mitigate the effects of different charge capacity and different charge and discharge rates for each particular battery in the battery pack. In many cases, cells with large capacity differences are only charged and discharged in parallel. To support this, battery management systems will often monitor the charge level of each battery, and perform battery management functions accordingly.
One of the consequences of different cells within the battery pack having different capacities is that the power supply bus has a high variation in operating voltage over the duration of a particular charge. Therefore, power system components, such as voltage regulators, are designed to operate over a very wide power supply voltage range. The efficiency of such voltage regulators, however, may decrease as the difference between the input voltage and regulated voltage increases.